The present invention relates to a ball stud having a buckle portion adapted to buckle under an external stress. The present invention also relates to a method and an apparatus for producing the ball stud. The present invention further relates to a ball joint including such a ball stud.
Conventional methods of producing a ball stud, including a buckle portion adapted to buckle under an external stress, are disclosed in Japanese Patent Laid-open No. 1994-55237.
The ball stud production method disclosed in Japanese Patent Laid-open No. 1994-55237 produces a ball stud of a ball joint which is used as a steering mechanism in a steering system of an automobile. The conventional production method forms a buckle portion by swaging or rolling the portion of a bar-shaped material intended for buckling. The resulting buckle portion of the bar-shaped material is reduced in diameter by a predetermined percentage. The material to be processed is formed into a bar beforehand by cold forging.
The ball stud production method disclosed in Japanese Patent Laid-open No. 1994-55237 requires a heavy load to squeeze the bar-shaped material to form a buckle portion having an axial length sufficient for buckling. Since the buckle portion is formed by merely squeezing the rolling bar-shaped material, a heavy load is necessary. Such a heavy load not only requires a large processing machine, but also reduces the life span of the roller or processing jigs, requiring the frequent replacement of these jigs. The problems associated with the conventional method of ball stud production make the manufacture of the ball stud difficult, which consequently increases the production costs.